This invention relates to a guide device for guiding a movable part of an apparatus relative to a fixed part of the apparatus.
Guide devices taking the form of ball guides or of cross-roller guides have been used for some time to guide a movable part of an apparatus linearly relative to a fixed part of the apparatus. Such guide devices often comprise two parallel guide rails one of which is arranged on the movable part and the other of which is arranged on the fixed part. Each guide rail is provided with a longitudinal groove and a plurality of roller elements arranged in a cage are movable linearly between the two guide rails in the grooves. End stops are usually provided on the guide rails to limit movement of the cage.
A field of use of guide devices of this type is that of the linear guidance of specimen clamping means in microtomes. In this case the movable part comprises the specimen clamping means while the fixed part comprises a base part of the microtome or a housing of the microtome.
In rotary microtomes the specimen clamping means is usually guided by the guide device so as to be movable vertically upwardly and downwardly.
In another kind of microtome, the specimen clamping means is guided by the guide device forwardly and rearwrdly in the horizontal direction. Even after a plurality of forward and rearward movement, which may occur at a high speed, the cage with the roller elements is not biased towards any particular position on the guide rails.
In contrast to this, in rotary microtomes the force of gravity draws the cage and the roller elements downwardly. This downward movement of the cage and roller elements depends upon the number of vertical load cycles, i.e. the number of up-and-down movements of the specimen clamping means; it also depends upon the number of vertical strokes made per unit of time.
When the cage rests against the lower end stop after a long period of use, the guidance properties of the guide device are impaired. Normally the cage should be located centrally between the end stops on the guide rails, because the best possible guidance properties can only be obtained when the cage is in this central position.